The invention relates to an apparatus and a method for enabling the calibration and/or monitoring of a combustion process in a combustion engine involving detecting noise from the engine related to the combustion process.
The manufacture of a vehicle which is driven by a combustion engine usually involves calibration of the engine's fuel injection system. Such calibration is usually carried out by manual methods which may be complicated and time-consuming, particularly the calibration of a combustion process in a diesel engine which incorporates so-called unit injectors, i.e. a high-pressure pump in combination with an injection nozzle. Such unit injectors are arranged on each of the engine cylinders and each incorporates an individual electrical control. Each of these unit injectors has therefore to be individually calibrated so that it injects fuel into the respective combustion chamber at exactly the time when the engine crankshaft is in an optimum position for the combustion process.
During subsequent operation of the vehicle, usually there is no monitoring of the combustion process to check that combustion takes place correctly and at the right time. Any checks are usually carried out only on certain predetermined servicing occasions or when an observant driver of the vehicle discovers that some fault has occurred in the combustion process, e.g. by the engine noise having changed. The probability of someone substantially immediately discovering a fault in the combustion process is slight and continuing operation without correcting the fault may lead to serious damage which may entail large repair costs or may cause the vehicle to be stationary at an inappropriate time or at an inaccessible location.